Video: Panic on London subway

WASHINGTON — Only two weeks after Britain's first homegrown suicide bombers killed 52 people in July 2005, four men allegedly tried to inflict more carnage.

Dramatic surveillance video is the first glimpse of what happened that day, when would-be bomber Ramzi Mohammed boarded an underground train and placed his backpack full of explosives next to a woman and a child in a stroller.

"The footage showing the bomber close to a woman with a baby is frankly quite nauseating," says Lord Toby Harris with the London Metropolitan Police Authority.

Mohammed fires the detonator, but the bomb fails to explode. Panicked passengers flee.

But a courageous fireman confronts the bomber, shouting, "What have you done, what have you done?" according to authorities.

Mohammed then claims that the explosive mixture leaking from his bag is not a bomb, but bread.

When the train reached the next station, Mohammed jumped out and raced away, chased by passengers.

Mohammed escaped that day, but was arrested eight days later and is now on trial along with others whose bombs also failed to detonate.

Released at the trial are photos showing the cell training in the bucolic British countryside, alongside other men in fatigues.

"The fact that these young men felt able to train almost openly on the U.K mainland soil...really shows the high level of their motivation," says Crispin Black, a former intelligence analyst with the British government.

A senior British intelligence official warns that some 200 possible terror cells are now under investigation and that British teenagers as young as 16 are being groomed to become suicide bombers.